Question

What is double fertilization? Give its significance.

Answer 1

Hint: In this process, one of the two male gametes borne by the pollen tube fuses with the egg cell nucleus to form the diploid zygote, and the other with the diploid central cell nucleus to form the endosperm.

Complete Answer:
All sexually reproducing organisms undergo fertilization. The fusion of male and female gametes for the development of zygote is known as fertilisation. Double fertilisation is a major feature of flowering plants.

After reaching the ovaries, the pollen tube enters the ovule through the micropyle and meets one of the synergids via the filiform apparatus. The pollen tube then discharges the two male gametes into the synergid cytoplasm. One of the male gametes fuses with the nucleus of the egg cell to form the diploid zygote. The other male gamete fuses with the two polar nuclei of the central cell and forms the triploid primary endosperm nucleus. The process of fertilization is known as double fertilization as it involves two forms of fusion in the embryo sac.

After triple fusion, the central cell forms the primary endosperm cell and grows into the endosperm while the zygote grows into an embryo. The primary endosperm cell then undergoes repeated division to form a triploid endosperm tissue. The cells of the endosperm tissue contain food materials which supplies nutrition to the developing embryo.

Note: Endosperm formation often precedes the development of the embryo. The mature dicotyledonous embryo has two cotyledons and an embryonic axis of epicotyl and hypocotyl. The monocotyledon embryos have a single cotyledon. After fertilisation, the ovaries develop into fruit and the ovules develop into seeds.